Green Iodination of Pyrazoles with Iodine/Hydrogen Peroxide in Water.

In this Letter, we describe a practical, green iodination of pyrazoles to form the corresponding 4-iodopyrazole derivatives. The reaction takes place in water, using only 0.5 equiv of iodine and 0.6 equiv of hydrogen peroxide, a system that generates water as the only reaction by-product.